ELECTRICAL POWER
4 marks · NormalA hairdryer uses the heating effect of an electric current. The label on the hairdryer states 'Power: 1200 W'.
Explain how the heating effect of current is used in a hairdryer.
Calculate the energy transferred by the hairdryer in 5 minutes of use.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
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(a) The current passes through a high-resistance wire in the hairdryer, causing it to heat up. The heated wire warms the air blown through the hairdryer. · must show reference to high resistance (or heating element), energy transfer to heat, wire becomes hot and heats air moved by hairdryer
(b) 360,000 J · must show correct use of E = P × t
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Marking points
M1 (a) · 1 mark · State that a high-resistance wire (heating element) heats up when current passes through it.
M2 (a) · 1 mark · Explain this heat is transferred to the air blown by the hairdryer.
M3 (b) · 1 mark · Use the formula E = P × t, converting time from minutes to seconds.
A1 (b) · 1 mark · Calculate and state the final energy value with correct units. (follow-through)
Worked solution
a) When current passes through the high-resistance wire in the hairdryer, it heats up due to the heating effect of current. This heat is transferred to air that is blown over the wire and out of the hairdryer to dry hair.
b) Power, P = 1200 W; Time, t = 5 min = 5 × 60 = 300 s.